Method for manufacturing electrode, classification system, and, electrode material

ABSTRACT

An electrode material containing active material powder is prepared. Dry classification of the electrode material is performed by a classifier. An electrode is manufactured by using the electrode material subjected to the dry classification. The classifier includes a mesh screen, a blade, and a motor. Breakage of the mesh screen is detected by monitoring either or both of an operation sound of the classifier and torque of the motor. The electrode material contained in the classifier will no longer be used for manufacturing of the electrode when breakage of the mesh screen is detected.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2022-007047 filed on Jan. 20, 2022, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to methods for manufacturing anelectrode, classification systems, and electrode materials.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2014-102967 (JP2014-102967 A) discloses a filter for filtering a slurry for forming anactive material layer.

SUMMARY

In the related art, an electrode is manufactured by application of aliquid paint. That is, a slurry is prepared by mixing an electrodematerial and a solvent. The electrode material can contain a binder, anelectrically conductive material, etc. in addition to active materialpowder. An electrode is manufactured by coating a surface of a basematerial with the slurry.

The solvent can dissolve the binder. The solvent also serves as adispersion media for solid particles. The solvent can include, forexample, an organic solvent. It is desired from the standpoint of, forexample, manufacturing cost, environmental loads, etc. to reduce solventusage associated with electrode manufacturing. Therefore, a process thatdoes not use slurry has also been proposed. For example, a powder paintis prepared by mixing active material powder and a binder. The powderpaint is wet powder or dry powder. An electrode can be manufactured bycoating a surface of a base material with the powder paint.

The active material powder is an agglomerate of active materialparticles. Active material particles cause electrode reactions. Theactive material powder ideally consists of active material particles.However, the active material powder can also contain a trace of foreignmatter. Foreign matter is unintended impurities. Foreign matter containsmetal. Foreign matter is considered to be generated by, for example,wear of equipment for producing active material powder. Foreign matteris in the form of particles. Foreign matter in the electrode mayadversely affect battery performance. Such an influence of foreignmatter tends to occur particularly when the foreign matter is coarseparticles. For example, battery self-discharge may increase.

Foreign matter can contain magnetic matter. Magnetic matter can include,for example, iron (Fe), iron oxides, and stainless steel (SUS)-derivedcomponents. In the related art, after the active material powder issynthesized, magnetic force separation (hereinafter referred to as“magnetic separation”) of the active material powder is performed toreduce magnetic matter. However, the separation efficiency of themagnetic separation is not high enough. For example, active materialparticles such as lithium cobalt oxide can also be magnetic. When activematerial particles are magnetic, the foreign matter separationefficiency may decrease. This is because the active material particlesare also attracted to a magnet. There is also foreign matter that is notmagnetic. For example, copper (Cu) is not magnetic. Hereinafter,“foreign matter containing magnetic matter and Cu” is sometimes referredto as “specific foreign matter.”

In the related art, a slurry containing an electrode material isfiltered with a filter to reduce specific foreign matter. However, thismethod cannot be applied to powder paints (wet powder, dry powder).

The present disclosure provides a method for manufacturing an electrode,a classification system, an electrode material, and an electrode thatreduce specific foreign matter (magnetic matter, Cu).

Technical configurations and functions and effects of the presentdisclosure will be described below. An action mechanism according to thepresent specification includes estimation. The action mechanism does notlimit the technical scope of the present disclosure.

1. In a method for manufacturing an electrode according to a firstaspect of the present disclosure,

an electrode material containing active material powder is prepared,dry classification of the electrode material is performed by aclassifier, andan electrode is manufactured by using the electrode material subjectedto the dry classification.The classifier includes a mesh screen, a blade, and a motor. The meshscreen has a tubular outer shape. The mesh screen is electricallyinsulating. The mesh screen is configured to separate coarse particlesfrom the electrode material. The blade is configured to press theelectrode material against the mesh screen. The motor is configured torotate the blade along an inner peripheral surface of the mesh screen.Performing the dry classification of the electrode material by theclassifier includes detecting breakage of the mesh screen by monitoringeither or both of an operation sound of the classifier and torque of themotor. Performing the dry classification of the electrode material bythe classifier includes stopping using the electrode material containedin the classifier for manufacturing of the electrode when the breakageof the mesh screen is detected.

According to the new knowledge of the present disclosure, specificforeign matter (magnetic matter, Cu) is coarse particles. The coarseparticles can be separated from the electrode material by the dryclassification. The dry classification can have high separationefficiency as compared to the method in which the slurry is filteredwith a filter. That is, the specific foreign matter can be reduced ascompared to the related art.

A mesh screen is used in the dry classification. Mesh screens tend tobreak easily. A broken mesh screen may allow the specific foreign matterto enter an electrode. That is, there is room for improvement in qualitystability.

One possible method to detect breakage of a mesh screen is to monitor achange in electrical resistance of a mesh screen. That is, electricallyconductive properties are given to the mesh screen. The electricalresistance of the mesh screen can increase when the mesh screen isbroken. Breakage of the mesh screen can therefore be detected by anincrease in electrical resistance. However, the electrode material cancontain an electrically conductive material. When the electrode materialcontains an electrically conductive material, breakage of the meshscreen may not be able to be detected.

Therefore, breakage of the mesh screen is detected by the operationsound of the classifier and the torque of the motor. Breakage of themesh screen can thus be detected even when the electrode materialcontains an electrically conductive material. By detecting breakage ofthe mesh screen, an electrode with a reduced content of specific foreignmatter can be stably manufactured. That is, the quality is expected tobe stabilized.

2. The electrode material may contain an electrically conductivematerial.

3. Performing the dry classification of the electrode material by theclassifier may include detecting a frequency component derived from thebreakage of the mesh screen by analyzing a frequency of the operationsound.

4. Performing the dry classification of the electrode material by theclassifier may include determining that the breakage has occurred whenthe torque falls out of a reference range.

5. Manufacturing the electrode by using the electrode material subjectedto the dry classification may include

preparing a paint containing the electrode material, andcoating a surface of a base material with the paint.The paint may contain, in addition to the electrode material, at leastone selected from the group consisting of an electrically conductivematerial, a solid electrolyte, a binder, and an additive.

6. The paint may have a solid content of 70% to 100% by mass fraction.

The paint with a solid content of 70% to 100% can be a powder paint (wetpowder, dry powder). A liquid paint (slurry) can have a solid contentof, for example, 60% or less.

7. The classifier may be stopped when it is determined that the breakagehas occurred.

The mesh screen may be replaced after stopping the classifier.Operation of the classifier may be resumed after replacing the meshscreen.

8. A second aspect of the present disclosure relates to a classificationsystem that performs dry classification of an electrode material. Theclassification system includes a classifier and a detector.

The classifier includes a mesh screen, a blade, and a motor. The meshscreen has a tubular outer shape. The mesh screen is electricallyinsulating. The mesh screen is configured to separate coarse particlesfrom the electrode material. The blade is configured to press theelectrode material against the mesh screen. The motor is configured torotate the blade along an inner peripheral surface of the mesh screen.The detector is configured to detect breakage of the mesh screen bymonitoring either or both of an operation sound of the classifier andtorque of the motor.

9. The detector may be configured to detect a frequency componentderived from the breakage by analyzing a frequency of the operationsound.

10. The detector may be configured to determine that the breakage hasoccurred when the torque falls out of a reference range.

11. The classification system may further include a controller. Thecontroller may be configured to stop the classifier when the breakage isdetected by the detector.

12. The detector may be configured to determine that the electrodematerial contained in the classifier is defective when the breakage isdetected.

The detector may be configured to redetermine that the electrodematerial determined to be defective is non-defective when the electrodematerial determined to be defective is subjected again to the dryclassification.

13. A third aspect of the present disclosure relates to an electrodematerial that includes active material powder. A content of magneticmatter in the active material powder is 4 ppm or less by mass fraction.A content of copper in the active material powder is 1 ppm or less bymass fraction.

14. A fourth aspect of the present disclosure relates to an electrodeincluding the electrode material of the third aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a block diagram of a classification system according to anembodiment;

FIG. 2 is a first schematic sectional view showing an example of aclassifier according to the embodiment;

FIG. 3 is a second schematic sectional view showing an example of theclassifier according to the embodiment;

FIG. 4 is a schematic flowchart of a method for manufacturing anelectrode according to the embodiment;

FIG. 5 is a schematic view illustrating a first coating method; and

FIG. 6 is a schematic view illustrating a second coating method.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure (hereinaftersometimes simply referred to as the “embodiment”) and examples of thepresent disclosure (hereinafter sometimes simply referred to as the“examples”) will be described. However, the embodiment and the examplesare not intended to limit the technical scope of the present disclosure.

Definition of Terms, Etc.

In the present specification, the terms “comprise,” “include,” “have,”and variations thereof (e.g., “composed of”) are open-ended. When any ofthe open-ended terms is used, it means that additional elements may ormay not be included in addition to essential elements. The term “consistof” is closed-ended. However, even when the closed-ended term is used,it does not mean that additional elements such as normally accompanyingimpurities and elements irrelevant to the technique of the presentdisclosure are excluded. The term “substantially consist of” issemi-closed-ended. When the semi-closed-ended term is used, it meansthat it is allowed to add elements that do not substantially affect thebasic and novel characteristics of the technique of the presentdisclosure.

In the present specification, the words such as “may” and “can” are usedin a permissive sense, meaning that “it is possible,” rather than in amandatory sense, meaning “must.”

In the present specification, elements in a singular form can also beplural unless otherwise specified. For example, the term “particle” canmean not only “one particle” but also an “agglomerate of particles(powder, powdery material, or group of particles).”

In the present specification, the order in which a plurality of steps,actions, operations, etc. included in various methods is performed isnot limited to the described order unless otherwise specified. Forexample, a plurality of steps may proceed in parallel. For example, theorder of a plurality of steps may be reversed.

In the present specification, the numerical ranges such as “m % to n %”are inclusive ranges including their upper and lower limit values unlessotherwise specified. That is, “m % to n %” indicates the numerical rangeof “m % or more and n % or less.” Further, “m % or more and n % or less”includes “more than m % and less than n %.” A numerical value selectedas desired from the numerical range may be set to a new upper limitvalue or a new lower limit value. For example, a new numerical range maybe set by combining a numerical value in the numerical range and anumerical value shown in a different part of the present specification,in a table, in the drawings, etc.

In the present specification, all numerical values should be interpretedas having the term “about” in front of them. The term “about” can mean,for example, ±5%, ±3%, or ±1%. All numerical values can be approximatevalues that can vary depending on the manner in which the technique ofthe present disclosure is used. All numerical values can be expressed insignificant figures. A measured value can be an average value of aplurality of measurements. The number of measurements may be three ormore, five or more, or ten or more. It is generally expected that thelarger the number of measurements, the higher the reliability of theaverage value. A measured value can be rounded off based on the numberof significant figures. A measured value can include an error etc. dueto, for example, the detection limit of a measuring device.

In the present specification, when a compound is represented by astoichiometric composition formula (e.g., “LiCoO₂”), the stoichiometriccomposition formula is merely a representative example of the compound.The compound may have a non-stoichiometric composition. For example,when lithium cobalt oxide is represented by “LiCoO₂,” lithium cobaltoxide is not limited to the composition ratio of “Li:Co:O=1:1:2” and cancontain lithium (Li), cobalt (Co), and oxygen (O) at any compositionratio, unless otherwise specified. Moreover, doping with a traceelement, substitution with a trace element, etc. can be allowed.

Geometric terms as used in the present specification (e.g., “parallel,”“perpendicular,” “orthogonal,” etc.) should not be interpreted in astrict sense. For example, the term “parallel” may refer to the statedeviating slightly from “parallel” in a strict sense. Geometric terms asused in the present specification may include, for example, tolerances,variations, etc. in terms of design, work, manufacturing, etc. Thedimensional relationships in the drawings may not match the actualdimensional relationships. The dimensional relationships (length, width,thickness, etc.) in the drawings may have been changed in order tofacilitate understanding of the technique of the present disclosure.Moreover, a part of the configurations may have been omitted.

The term “electrode” as used in the present specification is a generalterm for positive and negative electrodes. An electrode may be apositive electrode or a negative electrode. Electrodes can be applied toany desired battery system. In the embodiment, an example in whichelectrodes are applied to a lithium-ion battery will be described.

As used in the present specification, “D50” indicates the particle sizeat which the cumulative frequency reaches 50% in a volume-based particlesize distribution when counted from the smallest particle size.Moreover, “D99” indicates the particle size at which the cumulativefrequency reaches 99% in a volume-based particle size distribution whencounted from the smallest particle size. D50 and D99 can be measured bya laser diffraction method.

In the present specification, particles have a minor axis and a majoraxis. The “major axis” refers to the distance between the farthest twopoints on the contour line of a particle image. The “minor axis” refersto the diameter orthogonally crossing the line segment of the major axisat the midpoint of the line segment. The minor axis is sometimes equalto the major axis.

The term “solid content” as used in the present specification refers tothe total mass fraction of solid components in a paint. A componentdissolved in a solvent (e.g., a polymer binder) is regarded as a solidcomponent.

The term “slurry” as used in the present specification refers to adispersed system of a solid (powder) in a liquid (solvent). The term“wet powder” refers to a dispersed system of a liquid (solvent) in asolid (powder).

In the present specification, the “volume resistivity (Ω·cm)” of powdercan be measured by, for example, any of the “MCP-PD” series of powderresistivity analyzer made by Nittoseiko Analytech Co., Ltd. (or anequivalent product). The amount of sample is 2.0 g. The measurement loadis 20 kN.

Classification System

FIG. 1 is a block diagram of a classification system according to theembodiment. Hereinafter, the “classification system according to theembodiment” is sometimes simply referred to as the “classificationsystem.” A classification system 1000 includes a classifier 100 and adetector 200. The classification system 1000 may further include, forexample, a controller 300. The classifier 100, the detector 200, and thecontroller 300 may be separate and independent of each other, or may beintegrated and indivisible.

Classifier

FIG. 2 is a first schematic sectional view showing an example of theclassifier according to the embodiment. The classifier 100 performs dryclassification of an electrode material (powder material 10). Theclassifier 100 includes a housing 110, a mesh screen 120, blades 130, arotor 140, and a motor 150.

The housing 110 includes a body portion 111, a supply portion 112, afirst discharge portion 113, and a second discharge portion 114. Thebody portion 111 has a tubular outer shape. The body portion 111 mayhave a cylindrical outer shape. The body portion 111 houses the meshscreen 120, the blades 130, and the rotor 140. The supply portion 112extends so as to guide the powder material 10 into the body portion 111.The first discharge portion 113 is located below the body portion 111.Fine particles 11 are discharged from the first discharge portion 113.The second discharge portion 114 is located on the side in the axialdirection (Y-axis direction) of the body portion 111. Coarse particles12 are discharged from the second discharge portion 114. The seconddischarge portion 114 extends so as to guide the coarse particles 12downward.

The mesh screen 120 has a tubular outer shape. The mesh screen 120 mayhave, for example, a cylindrical outer shape. The mesh screen 120 islocated inside the body portion 111. The axis of the mesh screen 120 maycoincide with the axis of the body portion 111.

The mesh screen 120 is a mesh sieve. The mesh screen 120 separates thecoarse particles 12 from the powder material 10. The size of the coarseparticles 12 to be separated can be determined by the mesh size of themesh screen 120. The mesh size of the mesh screen 120 can be adjusted sothat the coarse particles 12 (specific foreign matter) are not allowedto pass through the mesh screen 120 and the fine particles 11 (electrodematerial) are allowed to pass through the mesh screen 120.

The fine particles 11 (electrode material) can have a D99 of less than50 μm. The fine particles 11 may have a D99 of, for example, 30 μm to 40μm. The coarse particles 12 (specific foreign matter) may have a minoraxis of, for example, 50 μm or more. The minor axis of the coarseparticles 12 may be, for example, two to 10 times, two to five times, ortwo to three times the D99 of the fine particles 11.

The mesh screen 120 is electrically insulating. The mesh screen 120 maybe made of, for example, resin. The mesh screen 120 may be composed of,for example, at least one selected from the group consisting ofpolyester, polyamide, and polyarylate.

The motor 150 rotates a shaft 151. The shaft 151 is inserted through therotor 140. Rotation of the shaft 151 causes the rotor 140 to rotate. Theaxes of the shaft 151, the rotor 140, and the mesh screen 120 maycoincide with each other.

The rotor 140 includes a screw portion 141. The screw portion 141 islocated below the supply portion 112. The screw portion 141 spirallyextends on the surface of the rotor 140 along the rotation axis of therotor 140. As the rotor 140 rotates, the screw portion 141 transportsthe powder material 10 into the body portion 111.

The blades 130 are connected to the rotor 140. Rotation of the shaft 151causes the blades 130 to rotate along the inner peripheral surface ofthe mesh screen 120.

FIG. 3 is a second schematic sectional view showing an example of theclassifier according to the embodiment. The section of FIG. 3 isorthogonal to the rotation axis of shaft 151. The blades 130 may extendin, for example, a radial pattern from the shaft 151 toward the innerperipheral surface of the mesh screen 120. The blades 130 may be, forexample, in the shape of a plate. As the blades 130 move along the innerperipheral surface of the mesh screen 120, the powder material 10 isdispersed onto the inner peripheral surface of the mesh screen 120. Thepowder material 10 is also pressed against the mesh screen 120. The fineparticles 11 in the powder material 10 pass through the mesh screen 120and are discharged from the first discharge portion 113. The coarseparticles 12 in the powder material 10 cannot pass through the meshscreen 120. The coarse particles 12 move along the inner peripheralsurface of the mesh screen 120 in the Y-axis direction. The coarseparticles 12 are discharged from the second discharge portion 114.

For example, as the blades 130 press the powder material 10 against themesh screen 120, an impact is applied to the mesh screen 120. Forexample, this impact may break the mesh screen 120. If the classifier100 continues to operate after the mesh screen 120 is broken, the coarseparticles 12 (specific foreign matter) may enter the first dischargeportion 113 (non-defective side).

Detector

The detector 200 detects breakage of the mesh screen 120. The brokenmesh screen 120 can change the operation sound of the classifier 100.The broken mesh screen 120 can change the torque of the motor 150. Thedetector 200 detects breakage of the mesh screen 120 by monitoringeither or both of the operation sound of the classifier 100 and thetorque of the motor 150. The detector 200 may monitor either theoperation sound or the torque, or may monitor both the operation soundand the torque.

The detector 200 may include, for example, a sound sensor (not shown)and an analyzer (not shown). The sound sensor measures the operationsound of the classifier 100. The analyzer collects and analyzes data onthe operation sound. The analyzer may analyze, for example, thefrequency of the operation sound. The analyzer may decompose the data onthe operation sound into frequency components by, for example, FastFourier Transformation (FFT). Of the frequency components thus obtained,the frequency component derived from breakage of the mesh screen 120 canbe identified. Breakage of the mesh screen 120 can be detected bydetecting this frequency component.

The detector 200 may include, for example, a torque sensor. The torquesensor measures the torque of the motor 150. The torque sometimesincreases when the mesh screen 120 is broken. The torque sometimesdecreases when the mesh screen 120 is broken. For example, a referencerange (lower limit value, upper limit value) may be set for the torque.The torque can change within the reference range during steadyoperation. The torque may fall out of the reference range when the meshscreen 120 is broken. It may be determined that the mesh screen 120 isbroken when the torque falls out of the reference range.

Controller

The controller 300 can control the operation and cooperation of eachdevice. For example, the controller 300 may stop operation of theclassifier 100 when the detector 200 detects breakage of the mesh screen120. For example, the controller 300 may determine that the electrodematerial contained in the classifier 100 is defective when the detector200 detects breakage of the mesh screen 120. For example, the controller300 may cause the electrode material contained in the classifier 100 tobe discharged into the second discharge portion 114 (defective side)when the detector 200 detects breakage of the mesh screen 120.

The defective material may be subjected again to the dry classification.The defective material subjected again to the dry classification may bedetermined to be a non-defective material.

Method for Manufacturing Electrode

FIG. 4 is a schematic flowchart of a method for manufacturing anelectrode according to the embodiment. Hereinafter, the “method formanufacturing an electrode according to the embodiment” is sometimessimply referred to as the “manufacturing method.” The manufacturingmethod includes “(a) preparation of electrode material,” “(b) dryclassification,” and “(c) manufacturing of electrode.”

(a) Preparation of Electrode Material

The manufacturing method includes preparing an electrode material. Theelectrode material contains active material powder. The electrodematerial may consist of, for example, active material powder. Theelectrode material may contain an additional component(s). For example,the electrode material may contain, in addition to the active materialpowder, at least one selected from the group consisting of anelectrically conductive material, a solid electrolyte, a binder, and anadditive. The electrode material containing an additional component(s)such as a binder can also be referred to as “electrode mixture.”

For example, the electrode material may be prepared by mixing at leastone selected from the group consisting of an electrically conductivematerial, a solid electrolyte, a binder, and an additive with the activematerial powder. For example, the electrode material may be prepared bysimple dry mixing. For example, the active material powder and othermaterial(s) may be compounded by mechanochemical treatment etc.

Active Material Powder

The active material powder is a main component of the electrodematerial. In the electrode material, the active material powder mayaccount for, for example, 50% to 100% by mass fraction. For example, theactive material powder may have a D50 of, for example, 1 μm to 30 μm, or5 μm to 20 μm.

The active material powder may be, for example, powder of a positiveelectrode active material. The positive electrode active material maycontain, for example, at least one selected from the group consisting ofLiCoO₂, LiNiO₂, LiMnO₂, LiMn₂O₄, Li(NiCoMn)O₂, Li(NiCoAl)O₂, andLiFePO₄. For example, “(NiCoMn)” in “Li(NiCoMn)O₂” indicates that thewhole of the elements inside the parentheses is 1 in terms of thecomposition ratio. The individual components of “(NiCoMn)” can becontained at any composition ratio as long as the whole is 1.Li(NiCoMn)O₂ may include, for example, Li(Ni_(1/3)Co_(1/3)Mn_(1/3))O₂,Li(Ni_(0.5)Co_(0.2)Mn_(0.3))O₂, and Li(Ni_(0.8)Co_(0.1)Mn_(0.1))O₂.

The active material powder may be, for example, powder of a negativeelectrode active material. The negative electrode active material maycontain, for example, at least one selected from the group consisting ofgraphite, soft carbon, hard carbon, silicon, silicon oxide, tin, tinoxide, and Li₄Ti₅O₁₂.

The active material powder may be magnetic. For example, activematerials containing a transition metal element such as Fe, cobalt (Co),or nickel (Ni) can be magnetic. For example, Li(NiCoMn)O₂, Li(NiCoAl)O₂,and LiFePO₄ can be magnetic.

Electrically Conductive Material

The electrically conductive material may be in the form of powder. Theelectrically conductive material may include, for example, electricallyconductive carbon particles and electrically conductive carbon fibers.The electrically conductive material may contain, for example, at leastone selected from the group consisting of carbon black, vapor-growncarbon fibers (VGCFs), carbon nanotubes (CNTs), graphene flakes, andgraphite. The carbon black may contain, for example, at least oneselected from the group consisting of acetylene black, furnace black,channel black, and thermal black. For example, 0.1 parts by mass to 10parts by mass of the electrically conductive material may be added per100 parts by mass of the active material powder.

Solid Electrolyte

The solid electrolyte may be in the form of powder. The solidelectrolyte may contain, for example, at least one selected from thegroup consisting of a sulfide solid electrolyte, an oxide solidelectrolyte, and a borohydride solid electrolyte. The solid electrolytemay contain, for example, at least one selected from the groupconsisting of Li₂S—P₂S₅, LiI—Li₂S—P₂S₅, LiBr—Li₂S—P₂S₅, andLiI—LiBr—Li₂S—P₂S₅. For example, 1 parts by volume to 100 parts byvolume of the solid electrolyte may be added per 100 parts by volume ofthe active material powder.

Binder

The binder may be in the form of powder. The binder may contain, forexample, at least one selected from the group consisting ofpolyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), apolyvinylidene difluoride-hexafluoropropylene copolymer (PVDF-HFP),styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide(PI), polyamideimide (PAI), and polyacrylic acid (PAA). For example, 0.1parts by mass to 10 parts by mass of the binder may be added per 100parts by mass of the active material powder.

Additive

The additive may be in the form of powder. The additive can have anydesired function. The additive may contain, for example, lithiumphosphate. For example, 0.01 parts by mass to 10 parts by mass of theadditive may be added per 100 parts by mass of the active materialpowder.

Electrically Conductive Material

The electrically conductive material can interfere with detection ofbreakage of the mesh screen by the classifier from a change inelectrical resistance. Since the manufacturing method uses theclassification system described above, breakage of the mesh screen canalso be detected when the electrode material contains the electricallyconductive material. The electrically conductive material may have avolume resistivity of, for example, less than 1×10² Ω·cm. Table 1 belowshows the relationship between the volume resistivity of variousmaterials and whether detection of breakage from a change in electricalresistance is possible. There is a tendency that, when the volumeresistivity is less than 1×10² Ω·cm, it is difficult to detect breakagefrom a change in electrical resistance.

TABLE 1 Volume Detection of Mesh Screen Resistivity Breakage from Changein Material (Ω · cm) Electrical Resistance Positive LiFePO₄ <1 × 10² NotPossible Electrode Active Material Positive Li(NiCoMn)O₂ >1 × 10²Possible Electrode Active Material Negative Natural <1 Not PossibleElectrode Graphite Active Material Electrically Acetylene <1 NotPossible Conductive Black Material Additive Lithium >1 × 10⁶ PossiblePhosphate

(b) Dry Classification

The manufacturing method includes performing dry classification of theelectrode material by the classifier. A material to be subjected to thedry classification may be only the active material powder, or may be theelectrode mixture. The dry classification of the manufacturing methodcan be performed by the classification system described above. Coarseparticles (specific foreign matter) can be separated from the electrodematerial by the dry classification. When breakage of the mesh screen isdetected while the classifier is in operation, the electrode materialcontained in the classifier at that time will not be used for electrodemanufacturing.

Electrode Material

The electrode material with a reduced content of specific foreign matter(magnetic matter, Cu) can be manufactured by the dry classification. Thecontent of the magnetic matter in the electrode material is 4 ppm orless by mass fraction. The magnetic matter can include, for example, Fe,iron oxide, and SUS-derived components. The SUS-derived components mayinclude, for example, Ni, chromium (Cr), and manganese (Mn). The contentof the magnetic matter may be, for example, 2.2 ppm or less, 1.9 ppm orless, 1.8 ppm or less, or 1.3 ppm or less. The content of the magneticmatter may be zero.

The content of Cu in the electrode material is 1 ppm or less by massfraction. The content of Cu may be zero.

Method for Quantifying Magnetic Matter

The magnetic matter can be quantified by the following procedure.

(1)N-methyl-2-pyrrolidone (NMP) is prepared as a dispersion medium. Theelectrode material is prepared as a sample. The sample is dispersed inthe dispersion medium by a mixer. A particle dispersion is thusprepared.(2) A bar magnet is immersed in the particle dispersion to collectmagnetic matter contained in the particle dispersion.(3) The bar magnet is removed from the particle dispersion. The magneticmatter attracted to the bar magnet is recovered. The magnetic matter maybe recovered using, for example, an adhesive tape.(4) The maximum diameter (dmax) of the magnetic matter and the particlecount of the magnetic matter are measured using a microscope.(5) The volume of the magnetic matter can be obtained by regarding themagnetic matter as spheres with a diameter of dmax. The density of themagnetic matter can be obtained from the composition of the magneticmatter. The mass fraction of the magnetic matter can be obtained fromthe volume, particle count, and density of the magnetic matter.

Method for Quantifying Cu

Cu can be quantified by the following procedure. It should be noted that“1 ppm” can be the detection limit in this procedure.

(1) The electrode material is prepared as a sample. A solution is formedby acid digestion of the sample.(2) The solution is filtered to recover the residue and the filtrate.(3) The residue is incinerated. After alkali fusion of the ash, acidextraction is performed.(4) A sample liquid is prepared by mixing the filtrate obtained in (2)and the extract obtained in (3). The volume of the sample solution isadjusted.(5) The sample solution is analyzed by inductively coupled plasma massspectrometry (ICP-MS). The mass fraction of Cu is thus measured.

(c) Manufacturing of Electrode

The manufacturing method includes manufacturing an electrode by usingthe electrode material subjected to the dry classification.

(c1) Preparation of Paint

The manufacturing method may include, for example, preparing a paint.The paint contains the electrode material. For example, the electrodematerial in a dry state may be used as it is as the paint. For example,wet powder may be prepared by mixing the electrode material and asolvent. The wet powder may contain, for example, granules (agglomerateof granulated particles).

Solvent

The solvent is liquid. The solvent can facilitate particle agglomerationof the wet powder. The solvent may contain, for example, water and anorganic solvent. The solvent may contain a component that can dissolvethe binder. The solvent may contain, for example, at least one selectedfrom the group consisting of water, butyl butyrate, and NMP.

(c2) Coating

The manufacturing method may include, for example, coating a surface ofa base material with the paint. Any desired coating method can be usedin the manufacturing method. A first coating method and a second coatingmethod, which will be described later, are merely by way of example. Forexample, coating may be continuously performed by a roll-to-roll method.Such continuous coating is expected to improve productivity.

Base Material

The base material may be, for example, in the form of a sheet. The basematerial may be, for example, an electrode current collector. The basematerial may contain, for example, metal foil. The metal foil maycontain, for example, at least one selected from the group consisting ofaluminum (Al), Cu, Ni, titanium (Ti), Cr, and Fe. The base material maybe, for example, Al foil or Cu foil. The base material may have athickness of, for example, 5 μm to 50 μm, or 10 μm to 30 μm.

First Coating Method

FIG. 5 is a schematic view illustrating the first coating method. Thefirst coating method is similar to liquid film transfer. In the firstcoating method, a paint 20 may be, for example, wet powder. The paint 20may have a solid content of, for example, 70% to 90%.

Three rolls are used in the first coating method. For example, a firstroll 2101, a second roll 2102, and a third roll 2103 may be arrangedside by side in the horizontal direction. The rotation axes of the rollsare parallel. The arrow shown in each roll indicates the rotationaldirection of that roll.

There is a first gap AB between the first roll 2101 and the second roll2102. There is a second gap BC between the second roll 2102 and thethird roll 2103.

The paint 20 is supplied into the first gap AB. An active material layer32 is formed as the paint 20 is leveled in the first gap AB. The secondroll 2102 transports the active material layer 32 into the second gapBC. The third roll 2103 transports a base material 31. The activematerial layer 32 is transferred to the base material 31 in the secondgap BC. That is, an electrode 30 including the active material layer 32and the base material 31 can be manufactured.

Second Coating Method

FIG. 6 is a schematic view illustrating the second coating method.Electrostatic coating is performed in the second coating method. In thesecond coating method, the paint 20 may be, for example, dry powder. Thepaint 20 may have a solid content of, for example, 90% to 100%.

The rotation axes of a first roll 2201, a second roll 2202, and a thirdroll 2203 are parallel. The third roll 2203 may be located verticallyabove the first roll 2201. A power supply 2204 forms an electric fieldbetween the first roll 2201 and the third roll 2203. The first roll 2201is provided with a magnet.

The paint 20 is supplied to a container 2205. The paint 20 may bestirred in the container 2205. For example, a ferromagnetic material maybe mixed with the paint 20 in the container 2205. The paint 20 isattracted to the first roll 2201 by a magnetic force F1 from the firstroll 2201. The first roll 2201 transports the paint 20. A substantiallyconstant amount of the paint 20 is supplied into the gap between thefirst roll 2201 and the third roll 2203 as a squeegee 2206 scrapes off apart of the paint 20.

The second roll 2202 transports the base material 31. The base material31 is supplied into the gap between the first roll 2201 and the thirdroll 2203.

An electric field is formed in the gap between the first roll 2201 andthe third roll 2203 so that an electrostatic force F2 acting on thepaint 20 is greater than the magnetic force F1 acting on the paint 20.The paint 20 is separated from the first roll 2201 by the electrostaticforce F2. The paint 20 then flies toward the third roll 2203 due to theelectrostatic force F2. The base material 31 is supported on the surfaceof the third roll 2203. The active material layer 32 can be formed asthe paint 20 adheres to the surface of the base material 31. That is,the electrode 30 including the active material layer 32 and the basematerial 31 can be manufactured.

Electrode

The electrode (primary sheet) can be manufactured in the mannerdescribed above. When the paint (active material layer) contains asolvent, the electrode may be dried. The active material layer may befixed to the base material by, for example, applying either or both ofpressure and heat to the active material layer.

The electrode may also be compressed to a predetermined thicknessaccording to the battery design. The electrode may be cut into apredetermined planar shape according to the battery design.

The active material layer may be formed only on one surface of the basematerial. The active material layer may be formed on both front and backsurfaces of the base material. The active material layer may have athickness of, for example, 10 μm to 1000 μm. The active material layermay have a thickness of, for example, 50 μm to 200 μm.

The active material layer contains the electrode material. That is, theelectrode includes the electrode material. The electrode materialcontains the active material powder. In the electrode, the content ofthe magnetic matter in the electrode material can also be 4 ppm or less.In the electrode, the content of Cu in the electrode material can alsobe 1 ppm or less.

First Experiment

The following materials were prepared.

Active material powder: LiFePO₄Electrically conductive material: carbon nanotubes (CNTs)

Binder: CMC, SBR

Solvent: water

Manufacturing Example 1

The content of specific foreign matter (magnetic matter, Cu) in theactive material powder was measured. The results are shown in Table 2below.

Wet powder was produced by mixing the active material powder, theelectrically conductive material, the binder, and the solvent in aplanetary mixer. A three roll mill was prepared. The wet powder waskneaded by the three roll mill. The solid content of the wet powder was75% or more.

An electrode was manufactured by the first coating method (see FIG. 5 ).A test battery including electrodes was also manufactured. The testbattery was a small laminated battery.

Manufacturing Example 2

A test battery was manufactured in a manner similar to that ofManufacturing Example 1 except that magnetic separation of the activematerial powder was performed before production of the wet powder. Thecontent of specific foreign matter in the active material powder wasmeasured after the magnetic separation. The results are shown in Table 2below.

Manufacturing Example 3

A test battery was manufactured in a manner similar to that ofManufacturing Example 1 except that dry classification of the activematerial powder was performed before production of the wet powder. Thecontent of specific foreign matter in the active material powder wasmeasured after the dry classification. The results are shown in Table 2below.

Self-Discharge Test

Four test batteries (N1 to N4) were manufactured in each manufacturingexample. A self-discharge test was performed on each test battery. Theresults are shown in Table 2 below. In Table 2, “OK” means that thevoltage drop was 0.7 mV or less, and, and “NG” means that the voltagedrop was more than 0.7 mV.

TABLE 2 Manufacturing Manufacturing Manufacturing Example 1 Example 2Example 3 Process of Reducing Foreign Matter No Process Magnetic DryPerformed Separation Classification Content of Magnetic 5.2  2.5  1.3 Specified Matter (ppm)¹⁾ Foreign Cu (ppm) 1.4  1.2  ≤1²⁾ Matter Self- N1Voltage Drop 1.24 0.66 0.54 Discharge (mV) Test Judgement NG OK OK N2Voltage Drop 0.98 0.98 0.66 (mV) Judgement NG NG OK N3 Voltage Drop 1.541.02 0.52 (mV) Judgement NG NG OK N4 Voltage Drop 1.10 0.59 0.36 (mV)Judgement NG OK OK ¹⁾Mass fraction. The same applies to Table 3.²⁾Detection limit or less. The same applies to Table 3.

Results

There is a tendency that the higher the content of the specific foreignmatter, the larger the voltage drop. The content of the specific foreignmatter was the lowest in Manufacturing Example 3 (dry classification).The voltage drop in the self-discharge test was also the smallest inManufacturing Example 3.

Second Experiment

A classification system was prepared. The classification system includeda classifier and a detector. The detector was configured to detectbreakage of a mesh screen by monitoring either or both of the operationsound of the classifier and the torque of a motor.

Manufacturing Example 4

In Manufacturing Example 4, the classifier was operated for six hourswith the detector not in operation (OFF state). The content of thespecific foreign matter was measured for each of the active materialpowder after one-hour classification, the active material powder afterthree-hour classification, and the active material powder after six-hourclassification. The results are shown in Table 3 below.

Manufacturing Example 5

In Manufacturing Example 5, the classifier was operated for six hourswith the detector in operation (ON state). When the detector detectedbreakage of the screen mesh, the classifier was stopped, the activematerial powder being classified was discharged, and the screen mesh wasreplaced. The operation of the classifier was resumed after the activematerial powder and the screen mesh are replaced. The content of thespecific foreign matter was measured for each of the active materialpowder after one-hour classification, the active material powder afterthree-hour classification, and the active material powder after six-hourclassification. The results are shown in Table 3 below.

TABLE 3 Manufac- Manufac- turing turing Example 4 Example 5 Detector(detects breakage of mesh screen) OFF ON After 1 h Content of Magnetic1.4 2.2 Classifica- Specified Matter (ppm) tion Foreign Cu (ppm) ≤1 ≤1Matter After 3 h Content of Magnetic 1.9 1.8 Classifica- SpecifiedMatter (ppm) tion Foreign Cu (ppm) ≤1 ≤1 Matter After 6 h Content ofMagnetic 4.3 1.9 Classifica- Specified Matter (ppm) tion Foreign Cu(ppm) 1.1 ≤1 Matter

Results

There is a tendency that the quality (content of specific foreignmatter) is stabilized over a long period of time by detecting breakageof the screen mesh.

Additional Notes

The embodiment also supports a “method for manufacturing an electrodematerial.”

The method for manufacturing an electrode material includes thefollowing (a) and (b):(a) preparing an electrode material containing active material powder;and(b) manufacturing an electrode material by performing dry classificationof the electrode material by a classifier.The classifier includes a mesh screen, a blade, and a motor. The meshscreen has a tubular outer shape. The mesh screen is electricallyinsulating. The mesh screen is configured to separate coarse particlesfrom the electrode material. The motor is configured to rotate the bladealong an inner peripheral surface of the mesh screen. The blade isconfigured to press the electrode material against the mesh screen.The above (b) includes detecting breakage of the mesh screen bymonitoring either or both of an operation sound of the classifier andtorque of the motor.

The embodiment and the examples are illustrative in all respects. Theembodiment and the examples are not restrictive. The technical scope ofthe present disclosure includes all modifications that fall within themeaning and scope equivalent to the claims. For example, it is plannedfrom the beginning to extract desired configurations from the embodimentand the examples and combine the extracted configurations as desired.

What is claimed is:
 1. A method for manufacturing an electrode, themethod comprising: preparing an electrode material containing activematerial powder; performing dry classification of the electrode materialby a classifier; and manufacturing an electrode by using the electrodematerial subjected to the dry classification, wherein: the classifierincludes a mesh screen, a blade, and a motor; the mesh screen has atubular outer shape; the mesh screen is electrically insulating; themesh screen is configured to separate coarse particles from theelectrode material; the blade is configured to press the electrodematerial against the mesh screen; the motor is configured to rotate theblade along an inner peripheral surface of the mesh screen; performingthe dry classification of the electrode material by the classifierincludes detecting breakage of the mesh screen by monitoring either orboth of an operation sound of the classifier and torque of the motor;and performing the dry classification of the electrode material by theclassifier includes stopping using the electrode material contained inthe classifier for manufacturing of the electrode when the breakage ofthe mesh screen is detected.
 2. The method according to claim 1, whereinthe electrode material contains an electrically conductive material. 3.The method according to claim 1, wherein performing the dryclassification of the electrode material by the classifier includesdetecting a frequency component derived from the breakage by analyzing afrequency of the operation sound.
 4. The method according to claim 1,wherein performing the dry classification of the electrode material bythe classifier includes determining that the breakage has occurred whenthe torque falls out of a reference range.
 5. The method according toclaim 1, wherein: manufacturing the electrode by using the electrodematerial subjected to the dry classification includes preparing a paintcontaining the electrode material, and coating a surface of a basematerial with the paint; and the paint contains, in addition to theelectrode material, at least one selected from the group consisting ofan electrically conductive material, a solid electrolyte, a binder, andan additive.
 6. The method according to claim 5, wherein the paint has asolid content of 70% to 100% by mass fraction.
 7. The method accordingto claim 1, further comprising: stopping the classifier when it isdetermined that the breakage has occurred; replacing the mesh screenafter stopping the classifier; and resuming operation of the classifierafter replacing the mesh screen.
 8. A classification system forperforming dry classification of an electrode material, theclassification system comprising: a classifier; and a detector, wherein:the classifier includes a mesh screen, a blade, and a motor; the meshscreen has a tubular outer shape; the mesh screen is electricallyinsulating; the mesh screen is configured to separate coarse particlesfrom the electrode material; the blade is configured to press theelectrode material against the mesh screen; the motor is configured torotate the blade along an inner peripheral surface of the mesh screen;and the detector is configured to detect breakage of the mesh screen bymonitoring either or both of an operation sound of the classifier andtorque of the motor.
 9. The classification system according to claim 8,wherein the detector is configured to detect a frequency componentderived from the breakage by analyzing a frequency of the operationsound.
 10. The classification system according to claim 8, wherein thedetector is configured to determine that the breakage has occurred whenthe torque falls out of a reference range.
 11. The classification systemaccording to claim 8, further comprising a controller, wherein thecontroller is configured to stop the classifier when the breakage isdetected by the detector.
 12. The classification system according toclaim 8, wherein: the detector is configured to determine that theelectrode material contained in the classifier is defective when thebreakage is detected; and the detector is configured to redetermine thatthe electrode material determined to be defective is non-defective whenthe electrode material determined to be defective is subjected again tothe dry classification.
 13. An electrode material, comprising activematerial powder, wherein: a content of magnetic matter in the activematerial powder is 4 ppm or less by mass fraction; and a content ofcopper in the active material powder is 1 ppm or less by mass fraction.